The invention relates to a method for inserting press-in or rivet-type connecting elements in metal sheets or components manufactured from sheet metal, and to a connection between a metal sheet and a connecting element.
Methods for inserting connecting elements in metal sheets or in components manufactured from sheet metal by joining and subsequent pressing are known in the art. The connecting elements are generally rivet and/or press nuts or bolts (threaded or unthreaded) and can appropriately be referred to as press-in and/or rivet connecting elements.
After joining, i.e. after insertion of the joining section of the respective connective element in a joining opening (pre-punched hole) in the metal sheet or sheet metal component, the connecting element is fastened or anchored by being pressed with plastic deformation of the material of the sheet in the area of the joining opening in which the connecting element is to be anchored. For the connection between the metal sheet and the connecting element created by joining and pressing it is necessary that this connection has high stability against the connecting element being pressed out of the metal sheet due to axially exerted forces, in addition to high stability against twisting, i.e. it must have a sufficiently high torsional absorption. This is achieved, for example, by the fact that during pressing the material of the metal sheet yields into an undercut that already exists on the connecting element and/or is created during pressing. Especially in order to achieve the required high torsional absorption, ribs or raised areas that are present on the connecting element are formed into the metal sheet and/or the metal sheet is formed onto non-circular contours of the connecting element. For this purpose it is necessary to adjust the hardness of the metal sheet and of the connecting element made of steel so that the metal sheet has a lower hardness than that of the connecting element.
The joining and pressing of the connecting elements frequently is carried out using a so-called punching head in a tool, for example a follow-on tool, in which also the respective sheet metal part or component is manufactured from the metal sheet, e.g. by punching and/or bending.
In many technological fields, in particular in the automotive field, metal sheets with a high hardness, for example stainless steel sheets, are increasingly being used, i.e. metal sheets with a hardness that is at least the same as, and generally even higher than the hardness of the available press-in and/or rivet connecting elements, so that the known joining and pressing method can no longer be used.
It is an object of the invention is-to present a method that enables connections by joining and pressing with the required standards of quality especially with respect to press-out stability and torsional absorption also in the case of metal sheets with a hardness that is greater or at least equal to the hardness of the respective connecting element.